Generally, radio frequency identification (RFID) refers to a technology that incorporates the use of signals in the radio frequency (RF) portion of the electromagnetic spectrum to uniquely identify a tag. An RFID device is often referred to as a tag. Typically, interrogating devices (commonly referred herein as interrogators or readers) obtain information from wireless tags by sending a command to a tag and receiving a response from the tag. Typically, the interrogator device includes a transmitter to transmit RF signals to the tag and a receiver to receive tag modulated information from the tag. The transmitter and receiver can be combined as a transceiver which can use one or more antennas.
RFID transponders (commonly referred to herein as “tags”) in the form of labels, inlays, straps or other forms are widely used to associate an object with an identification code. Tags generally include one or more antennas with analog and/or digital electronic circuits that include communications electronics (such as an RF transceiver), data memory (for storing one or more identification codes), processing logic (such as a microcontroller) and one or more state storage devices. Examples of applications that can use RFID tags include luggage tracking, inventory control or tracking (such as in a warehouse), parcel tracking, access control to buildings or vehicles, etc.
Generally, there are three basic types of RFID tags. An active tag, having an independent power supply, includes its own radio frequency source for transmission. A battery-powered semi-passive tag also receives and reflects radio waves from the reader; however a battery powers the tag independent of receiving power from the reader.
A passive tag is a beam powered device which rectifies energy required for operation from radio waves generated by a reader and transmitted to the passive tag. For communication, the passive tag creates a change in reflectivity of the field which is reflected to and read by the reader. This is commonly referred to as backscattering.